X-ray CT apparatus

Abstract

An X-ray CT apparatus comprising: a scanner unit for rotating one or more X-ray sources for applying X-ray beams having different energy spectra to an object, and detectors disposed opposed to the X-ray sources for detecting transmitted X-ray data on the object, around the object while applying X-rays, reconstructing means for reconstructing a tomogram of the object by acquiring transmitted X-ray data on the object including the two or more different energy spectra by using the scanner, and display means for displaying the reconstructed tomogram; the X-ray CT apparatus further comprising input means for inputting information on an identification tissue of the object to be identified and a separate tissue to be separated from the identification tissue from the tomogram and scanning condition determining means for determining the scanning condition for identifying the identification tissue from the tomogram. With this, an optimum scanning condition of a multi-energy X-ray CT apparatus can be determined.

1. An X-ray CT apparatus comprising:
 a scanner unit rotating one or more X-ray sources for irradiating X-rays having a plurality of different energy spectra to an object to be examined, and detectors disposed facing the X-ray sources for detecting transmitted X-ray data of the object, around the object while irradiating X-rays; 
 reconstruction means for acquiring transmitted X-ray data of the object having two or more different energy spectra by the scanner unit, and reconstructing a tomographic image of the object; and 
 display means for displaying the reconstructed tomographic image, 
 characterized in further comprising: 
 input means for inputting the information on an identification tissue of the object to be identified from the tomographic image and a separate tissue to be separated from the identification tissue; and 
 scanning condition determining means for determining scanning condition for identifying the identification tissue from the tomographic image. 
 
     
     
       2. The X-ray CT apparatus according to  claim 1 , wherein the scanning condition determining means is irradiated X-ray spectrum selecting means which arbitrarily selects two or more energy spectra from the plurality of different energy spectra. 
     
     
       3. The X-ray CT apparatus according to  claim 2 , wherein the irradiated X-ray spectrum selecting means selects the tube voltage from the plurality of different energy spectra. 
     
     
       4. The X-ray CT apparatus according to  claim 3 , wherein the scanning condition determining means comprises calculation means for calculating the index related to the accuracy in identifying the identification tissue on the tomoraphic image reconstructed by acquiring transmitted X-ray data having the arbitrary two or more selected plurality of energy spectra. 
     
     
       5. The X-ray CT apparatus according to  claim 4 , wherein the calculation means calculates the index with respect to the combination of the plurality of tube voltages which generate the plurality of different energy spectra. 
     
     
       6. The X-ray CT apparatus according to  claim 5 , wherein the irradiated X-ray spectrum selecting means selects the combination of the tube voltages having the index with high accuracy from among the indexes. 
     
     
       7. The X-ray CT apparatus according to  claim 5 , wherein the display means displays the indexes in the form of a table chart with respect to the combinations of the plurality of tube voltages. 
     
     
       8. The X-ray CT apparatus according to  claim 4 , wherein:
 the scanning condition determining means comprises storing means for storing a plurality of different energy spectra and X-ray attenuation coefficient of a number of tissues of the object, and tissue selecting means for selecting a desired identification tissue from among the number of tissues and a separate tissue desired to be separated from the identification tissue; and 
 the calculation means comprises simulated image constructing means for generating a simulated image using the plurality of different energy spectra and X-ray attenuation coefficient of the identification tissue and separate tissue, histogram generating means for generating histograms indicating pixel distribution of the identification tissue and the separate tissue, and index calculating means for calculating the index from overlapping degree of the histograms of the identification tissue and the separate tissue. 
 
     
     
       9. The X-ray CT apparatus according to  claim 8 , wherein the simulated image constructing means comprises:
 effective energy calculating means for calculating the respective effective energies of the plurality of different energy spectra; 
 CT value calculating means for calculating a CT value of the identification tissue and the separate tissue using X-ray attenuation coefficient of the calculated effective energy, tomographic image noise calculating means for calculating amount of noise on the tomographic image calculated based on tube current values, and means for constructing a simulated image based on the CT value and amount of noise on the tomographic image. 
 
     
     
       10. The X-ray CT apparatus according to  claim 9 , wherein the tomographic noise calculating means comprises:
 means for calculating amount of noise on projection data based on the tube current values; and 
 conversion means for converting the noise of amount on projection data into the amount of noise on image data. 
 
     
     
       11. A scanning condition determining method in an X-ray CT apparatus comprising:
 (1) a step for inputting information on an identification tissue of an object to be identified and a separate tissue desired to be separated from the identification tissue on a tomographic image obtained by the X-ray CT apparatus; and 
 (2) a step for determining the scanning condition for identifying the identification tissue from the tomographic image. 
 
     
     
       12. The scanning condition determining method in the X-ray CT apparatus according to  claim 11 , wherein the step (2) is for selecting arbitrary two or more energy spectra from among the plurality of different energy spectra. 
     
     
       13. The scanning condition determining method in the X-ray CT apparatus according to  claim 12 , wherein the step (2) is for selecting the tube voltage which generates the plurality of different energy spectra. 
     
     
       14. The scanning condition determining method in the X-ray CT apparatus according to  claim 13 , wherein the step (2) includes:
 (3) a step for calculating an index related to the accuracy in identifying the identification tissue on the tomographic image reconstructed from transmitted X-ray data acquired using arbitrary two or more selected plurality of energy spectra. 
 
     
     
       15. The scanning condition determining method in the X-ray CT apparatus according to  claim 14 , wherein the step (3) calculates the index with respect to the combination of the plurality of tube voltages of the plurality of different energy spectra. 
     
     
       16. The scanning condition determining method in the X-ray CT apparatus according to  claim 15 , wherein the step (2) selects the combination of the tube voltages having the index with high accuracy from among the indexes. 
     
     
       17. The scanning condition determining method in the X-ray CT apparatus according to  claim 15 , wherein the step (2) includes a step for displaying the indexes in the form of a table chart with respect to the combinations of the plurality of tube voltages. 
     
     
       18. The scanning condition determining method according to  claim 14 , wherein the step (2) comprises:
 (4) a step for storing the plurality of different energy spectra and X-ray attenuation coefficient of the number of tissues of the object; and 
 (5) a step for selecting the desired identification tissue from among the number of tissues and a separate tissues desired to be separated from the identification tissue, and the step (3) includes: 
 (6) a step for constructing a simulated image using the plurality of different energy spectra and X-ray attenuation coefficients of the identification tissue and the separate tissue; 
 (7) a step for generating histograms indicating the pixel distribution of the identification tissue and the separate tissue from the simulated image obtained in the step (6); and 
 (8) a step for calculating the index from the overlapping degree of the histograms of the identification tissue and the separate tissue. 
 
     
     
       19. The scanning condition determining method according to  claim 18 , wherein the step (6) comprises:
 (9) a step for calculating the respective effective energies of the plurality of different energy spectra; 
 (10) a step for calculating a CT value of the identification tissue and the separate tissue using X-ray attenuation coefficient of the calculated effective energies; 
 (11) a step for calculating amount of noise on the tomographic image calculated based on current values; and 
 (12) a step for constructing a simulated image based on tomographic image noise calculating means, the CT values and amount of noise on the tomographic image. 
 
     
     
       20. The scanning condition determining method according to  claim 19 , wherein the step (11) includes:
 (13) a step for calculating amount of noise on projection data based on the tube current values; and 
 (14) a step for converting the amount of noise on projection data into amount of noise on image data.